Ferrite circulators for waveguides commonly have a pair of symmetrical dielectric spacers used either for centering a ferrite element in the height of the waveguide or to improve the thermal path from the ferrite element to a metal housing structure. For moderate power handling, the thermal path through one spacer is sufficient to cool the ferrite element, so only one of the two spacers might be bonded to the housing structure for ease of assembly. While the second spacer could be eliminated from a thermal standpoint, the dielectric loading the second spacer provides is often required to provide adequate radio frequency (RF) performance.
Mechanically, the stack-up of two spacers and one ferrite element must fit in the height of the waveguide, which provides a tolerancing issue. Tight tolerances must be held on the height of all of the parts, but parts are commonly scrapped during manufacture because the stack-ups are either too short or too tall to work correctly in the waveguide, either due to mechanical fit or RF performance issues.